The hitherto known processes for the preparation of diosone of the formula (2). Where Ac represents acetyl group have been described below.
i) Marker R. H, U.S. Pat., No. 2,409,293 1947. Chem. Abstr. 41, 1396f
In this method pseudodiosgenin diacetate of the formula (1) where Ac represents an acetyl group is oxidized with chromium trioxide in acetic acid at 28.degree. C. to get diosone of the formula (2) where Ac represents an acetyl group.
ii) Colin L. Hewatt. British Pat. 749, 697, May 30, 1956 Chem Abstr. 51, 1957, 28907.
In this method steroidal sapogenin or esters were converted first to pseudosapogenin which is then converted to pseudodiosgenin and finally the pseudodiosgenin is again oxidized with chromium trioxide to get pregnalien-3-ol-20 one acetate.
iii) John, M. Chemorda; William, V. Ruyle and Leon, Mendell. U.S. Pat. No. 3,136,758, (Cl 260-239.55) 1964. Chem Abstr. 61, 7081Q.
In this method 5,6-dichlorodiosgenin was oxidized with chromium trioxide in acetic acid and water to get 5,6-dichloro 16-dehydropregnenolone acetate.
iv) Ngo, Ngoc Khuyen, Nguyen, Van Dan. Tap Chi Hoa Hec 1976, 14 (1) 37-39 (Vietnam) Chem Abstr. 88, 191216z.
In this method 16 Dehydropregnenolone acetate (3) was prepared by boiling a solution of diosgenin in acetic anhydride and pyridine hydrochloride, cooling, adding aqueous sodium acetate followed by oxidation with potassium dichromate and boiling with aqueous sodium bisulphite extracting with petroleum ether to get the product.
v) Kavtardge L. K. Izv Akad Nauk Gruz S S R, Ser Khim 1984, 10 (3) 229-31 (Russ). Chem Abstr. 103, 123771e.
In this method too tigogenin is converted by conventional method to pseudodiosgenin and finally pseudodiosgenin is oxidized with chromium trioxide in acetic acid to give 3-hydroxy-5-pregnen-16-en-20-one.
vi) Micovic, I. V. Ivanovic, M. D and Platak, D. M. Synthesis, 1990, 591.
In this method diosgenin is converted to pseudodiosgenin diacetate by refluxing with acetic anhydride in presence of ammonium chloride and pyridine and pseudodiosgenin diacetate (PDA) is again oxidized by conventional method using chromium trioxide and acetic acid at 0-150.degree. C. to diosone which is finally hydrolysed by refluxing it in acetic acid to get 69% 16-dehydroprenenolone acetate.
In all these methods the major drawback is that the oxidizing agent contains chromium which is highly poisonous, costly and not echo friendly.